Technical Paper
the above mentioned inconveniences. Nevertheless, this new binder improves wear
resistance
www.ireng.org
of both, alumina-
spinel and alumina-magnesia castable as shown in a dynamic slag corrosion test in a rotary kiln (Figure 10 and 11). Formulations with the same total amount of spinel after firing and the same amount of CaO have been compared in this case. In the case of the
alumina-magnesia castable
the amount of free Magnesia could be reduced from 6.5% to 3% when CMA72 was used. CMA72, due to its micro-crystalline spinel content creates a higher strength after firing at equal total CaO content than the reference based on Secar®
71 and added spinel
powder. Typical dosage rates of CMA 72 are in the range of 12-18% for strongly slag loaded applications while addition rates of 8-12% to alumina- spinel castables are beneficial when thermal shocks are the predominant damage factor. In alumina-magnesia castables also higher contents of CMA72 result in good thermal shock resistance when just a small amount of silica fume is present to control expansion and prevent magnesia hydration [6]
.
Binder that improves performance and reduces re-bound of dry-gunning mixes
The dry-gunning method is an established technology despite its
inconvenient high rebound rate and relatively high water demand compared to vibrated or shotcreted castable. It allows installation of small quantities of material within a short period of time for example for repairs. Dry-gunning machines are largely available and easy to use. More sophisticated dry-gunning machines have been developed in recent years that also allow the installation of deflocculated castables to achieve lower porosity. Nevertheless, these machines are not so widely spread yet and the technology requires more sophisticated formulations with similar sensitivities as observed with LCC. A new binder has been developed that allows installation of gunning mixes with traditional machines but with reduced re-bound rates to minimize material consumption during installation. Furthermore it has a low water requirement that results in low porosity to enable high wear resistance.
AGGREGATES DEVELOPMENT
Also in the fields of aggregates new developments could lead to further cost optimizations. While for example castables for steel ladle applications use in most of the cases high density aggregates with low porosity, the weakest part of a castable with respect to penetration and corrosion is typically the matrix with much higher porosity than the aggregates. That raises the question if it wouldn’t be better to develop micro-porous high temperature resistant aggregates that could result in a weight reduction of a ladle lining. That could not only save refractory material but also energy due to lower thermal conductivity. First attempts into this direction have been made with a synthetic aggregate containing microcrystalline MA- spinel, calcium aluminate phases and micro-pores. Weight reduction in the
Figure 11: Corrosion of A-MA and A-M castables
range of 10% have been achieved without big impact on physical properties of the castable since the matrix remained unchanged. Further investigations are running to evaluate the wear resistance with these new aggregates.
Conclusion
The steel industry will continue to request refractory solutions with further increased performance/cost ratios per ton of steel. Innovations in the field of refractory raw materials are one important element assisting the refractory industry achieving these targets. Especially in the field of refractory castables the new raw material developments can help improving several aspects in a life of a castable, from more homogeneous and less aging sensitive dry-mixes, over more robust, reliable and repeatable installation and dry- out properties, up to new microstructure designs that enable a longer service life. New Active Compounds and Calcium Aluminate and Calcium Magnesium Aluminate binders can play an essential role in this regard. But also innovations in the field of aggregates offer new opportunities for the refractory industry to move the performance/cost ratio to new levels.
References
1.
www.worldsteel.org 2.
https://www.bloomberg.com/news/articles/2015-01-06/u-s-steel-to- idle-pipe-factories-after-oil-price-slump
3.
http://marketrealist.com/2015/02/steel-industrys-capacity-utilization- ratio-fell-3-year-low/
4. Wöhrmeyer, C., et al. New active compound range for refractory castables with superior robustness, ALAFAR 2016
5. Parr, C., et al. New solutions to increase the shelf life of low cement castables. ICR Aachen, 2010
6. Wöhrmeyer, C. et al. Thermal shock resistance of ladle castables, ISR Xi’an, 2016
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January 2018 Issue
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